Don't core dump when using CMAC with dgst.

We can't unfortunately print the CMAC cipher used without extending the API.

PR#2579

apps/dgst.c

@@ -529,7 +529,8 @@ int MAIN(int argc, char **argv)
 					EVP_PKEY_asn1_get0_info(NULL, NULL,
 						NULL, NULL, &sig_name, ameth);
 				}
-			md_name = EVP_MD_name(md);
+			if (md)
+				md_name = EVP_MD_name(md);
 			}
 		err = 0;
 		for (i=0; i<argc; i++)
@@ -641,7 +642,12 @@ int do_fp(BIO *out, unsigned char *buf, BIO *bp, int sep, int binout,
 	else 
 		{
 		if (sig_name)
-			BIO_printf(out, "%s-%s(%s)= ", sig_name, md_name, file);
+			{
+			BIO_puts(out, sig_name);
+			if (md_name)
+				BIO_printf(out, "-%s", md_name);
+			BIO_printf(out, "(%s)= ", file);
+			}
 		else if (md_name)
 			BIO_printf(out, "%s(%s)= ", md_name, file);
 		else